The invention relates to an ink only label, which is removable from a substrate to which it has been applied by washing with water or an aqueous alkaline solution and to a transfer label comprising a backing layer and the ink only label which is releasably attached to the backing layer.
The invention also relates to a container provided with an ink only label according to the invention and to a method of removing the ink only label from such a container.
More in particular the present invention is directed to a label for returnable plastic containers such as crates and more specifically to decorative promotional and/or informational labels suitable for use on plastic crates. Still more particularly, the invention is directed to a label composite which applies only the inks of the graphics to a polymeric substrate, having the ability to be removed from the substrate, without destructive treatment of the substrate surface, so that the substrate can be relabelled.
It is known in the packaging technology art to label containers such as plastic crates by providing a non-removable permanent image by a silk screen method. Such labels offer a highly durable finish with two or three color availability. This technique however offers limited colors, lacks the improved graphics that other labelling techniques offer, is not flexible in its ability to have graphic changes to meet market strategies leading to large inventories of obsolete units, tends to show signs of wear after about four trips (typical crate life expected at 60 return trips and is relatively expensive as compared to other label techniques.
When removable inks are to be applied to re-usable plastic crates by a screen printing or a tampon printing process, the inks have to be applied in the bottling plant, such as a brewery, which may lead to problems with respect to registration. Upon removal from the crates by means of crate washers, the inks will be dissolved in the washing liquid and in this way contaminate the crate washers. Furthermore the speed of application is limited, and curing of the inks requires a lot of space and long storage times prior to delivery.
A second way of labelling containers encompasses gluing printed paper labels to containers such as plastic crates or bottles at the time of filling and sealing. This type of label however offers little resistance to label damage from handling and exposure to moisture (wrinkling). Furthermore, paper labels are difficult to remove from crates, and tend to clog the crate washers available today. Upon removal of paper labels from plastic crates, a glue residue may be left on the crates.
A third technique for labelling containers, in particular glass bottles is based on the principles described in WO 90/05088. This method of labelling bottles provides a durable, highly impact resistant label and yet permits high definition label printing. A transfer label comprising a removable backing layer is provided which backing layer is reverse printed with a vinyl or acrylic ink which is cured and overprinted with adhesive. The label is applied to the container with its adhesive surface in contact therewith. The backing layer is separated from the transfer layer of the label for instance by the application of heat to either the container, the label or to both. The labelled container is then applied with a coating which is subsequently cured. The cured coating provides the required degree of impact resistance and durability. The disadvantage of permanently attached labels, is that when these labels get scratched or otherwise damaged, they cannot be easily removed from the bottles. Further, it is not possible to provide the same containers each time with new and/or different labels, which is desirable for promotional activities.
The need for returnable bottles and crates is a direct result of industry preference and government legislation with regard to returnable (refillable) containers in various parts in the world in lieu of one way packaging. In this type of recycling environment a whole new market has been created for the handling of packaged beverage containers. This is presently true of both refillable PET and glass bottle containers. Certain countries, European in particular, have invested large sums of money in the creation of distribution systems that rely heavily on the returnable crate concept.
Typically the only product presentation in such a recycling (refillable) market is that which can be printed on the exterior of the crate. Due to handling, space and storage considerations the only marketing, name brand, promotional, UPC code or other informational presentation is that which is printed on the exterior of the crate. The reason is that typically the crates are stacked at commercial outlets such as grocery stores with only the side and end panels showing. As such, the presentations on the said panels of the crates are the only distinguishing features from one product to another.
In the use of returnable crates it would be very interesting to be able to use one uniform crate for various different products or brands. However, this is only possible if there exists an easy and inexpensive method of providing an image or imprint on the crate, which is also easily removed after the crate is returned to the bottling line for refilling.
On the other hand, it is important that the label image or imprint on the crate is durable, especially during transport, storage and is durable even when subjected to humid conditions.
Accordingly it is an object of the invention to provide a label for a returnable plastic crate creating an imprint, or image on at least one of its surfaces, which is durable, scratch, wear, weather and moisture resistant during use, but which is easily removable during the crate washing operation upon return to the filler.
It is also an object of the invention that the label on the plastic container shall be impervious to handling contact and ambient storage conditions both outdoor and indoor.
It is also an object of the invention that the label, if desired, be readily and completely removed in the standard crate washer used when the plastic container is returned to the beverage plant for refilling.
It is also an object of the invention that the properties of the label with respect to removing it can be controlled, so that the label will not be removed or damaged in standard crate washing operations, but only under specific, more severe crate washing operations.
It is an object of the present invention that the labels incorporate a full range of graphics, from a simple one color up to a full photographic reproduction.
Finally it is also an object that the method be simple and low cost.
These and other objects are achieved by the ink-only label according to the present invention, said label at least consisting of an adhesive layer, an ink-only image layer and optionally a protective layer, wherein the label, when applied to a substrate, has a water permeability coefficient, as defined herein, which is sufficient to enable fast removal of the label from the substrate with water or an aqueous alkaline solution, without destructive treatment of the said substrate.
In order to provide the desired removal characteristics it has been found essential to control the water permeability characteristics of the label when applied to the substrate surface, such as a crate surface. On the one hand the water permeability must be sufficiently high to provide a speedy removal of the label through break-up and/or swelling of the material when immersed in or sprayed with water. On the other hand it should not be so high that the label becomes removed when subjected to normal ambient conditions. In effect the water permeability characteristics have been fine-tuned to provide a label that meets the criteria defined herein above.
The water permeability coefficient is defined as the amount of water that the label takes up, as a fraction of the dry weight of the label within a period of three hours immersion at 20xc2x0 C. The coefficient can be determined using the test method for the water uptake.
As indicated above the value for this coefficient should on the one hand be sufficient to enable removal of the label from the substrate with water, without destructive treatment of the said substrate, and on the other hand be such that during normal outdoor conditions the label remains intact and good-looking.
In general this means that the lower limit for the water permeability coefficient is 0.15, preferably 0.25 and most preferred 0.50. The upper limit for this coefficient is 2.50, preferably 1.35 and most preferred 1.00.
According to a preferred embodiment the label of the invention possesses a water uptake test value which is between 1 and 75 g water/m2 of label, typically about 5 g/m2. The water uptake test value is especially a measure for the resistance of the label against removal by soaking. The test is carried out as defined furtheron.
When the value is not more than 75 g/m2, the label is resistant to removal under ambient outdoor conditions, i.e. when the label has been applied to a crate which has been left in rainy conditions, the label will not become damaged or removed, at least to a substantial degree.
On the other hand, when the value is more than 1 g/m2, preferably more than 2.5 g/m2, the label can be removed sufficiently fast in a standard crate washing equipment.
Likewise the properties of the label can be determined using the pencil scratch test, which is also described in detail later, both under dry and wet conditions. In general test values for pencil hardness of at least 1 N indicate sufficient durability of the label under ambient (dry) conditions. Generally values between 1 and 10 N are acceptable, whereas lower values result in insufficient scratch resistance and values of over 7 N are indicative of labels that are not easily removed. After immersion in water the pencil hardness should drop to below 0.5 N within an acceptable period of time (10 min., preferably 3 min, more preferred 1 min.).
Another property of the label that is important for determining the ease of removal of the label from a substrate is the water vapor transmission rate per m2 per 24 h. This rate should of course be higher than 0, as otherwise no vapor transmission will occur (and in all likelihood no water uptake). In general, suitable labels have a water vapor transmission rate of at least 50. The upper limit of this rate is about 750, whereas a typical, suitable value is about 600 g/cm2/24 h.
The term xe2x80x9cink only labelxe2x80x9d is used herein to define a label that does not have a paper or plastic backing, but which comprises an image layer of ink, which is directly applied to a surface. Quite often the surface remains at least partly visible through the image layer. An ink only label may conveniently be applied to a surface by image transfer using a reverse printed label.
The label to be used in accordance with the present invention is essentially based on an ink image without a backing material. The ink image will adhered to the surface of the crate by an adhesive, and the surface of the image may be protected by a protective layer.
The present invention provides a distinct improvement over the prior art systems, which were based on paper or plastic labels. In order to remove these labels expensive high pressure equipment was necessary, especially in the case where labels were required on adjacent sides of the crate. Removal of the labels through simple soaking, as in the present invention, is virtually impossible. Further the residues of the labels have a tendency to clog the crate washing equipment.
The system of the present invention is less expensive and environmentally more friendly, as the residues of the ink only label are easily recovered from the water so that the water can be recycled.
The present invention also provides the possibility to use the label for scanning possibilities, for example by including a UPC (bar) code therein, which code may be used to define the recipient, the contents or any other information that is suitable. The system also allows the producer to reduce the stock of crates, as it is no longer necessary to keep stock crates of all brands or types. The system according to the present invention makes it possible for a producer to have only one type of crate for each type of material, for example a bottle, irrespective of the brand of the material. This makes it possible to reduce the stock of crates substantially. Of course the reduction would be even greater if the whole industry in a country or continent would decide to use the system.
In such a case many different producers (bottlers) of beverage containers would share common crates, and yet maintain individual market identification via the present invention. At the same time an improved user friendly and cost effective recycling system would be perfected. Such a system could be utilized on a national of even a multi-national level.
According to a preferred embodiment a transparent protective coating is present on top of the image layer. This coating improves the resistance of the label against environmental influences. Generally the material of the protective coating is compatible with the material of the ink. More preferably all materials, adhesive, ink and protective coating are at least partly based on acrylate polymers. In order to improve the durability of the label further, it may be advantageous that after application of the label (and the coating) one or more treatments are given. These treatments provide a coalescence of the materials of the various layers, resulting in improved service life, without, however, deteriorating the wash-off behaviour.
By careful selection of the composition of the label, the use of a protective coating and the nature of the post treatment, it is possible to steer the properties of the label, especially with respect to the behavior during crate washing. More specifically, it is possible to design the system in such a way, that the label is removed during standard crate washing. This means that after each return to the beverage filling plant, the label is removed and a new, optionally different, label may be applied. On the other hand, the label may be made so durable that it can not be removed or damaged during standard crate washing, but only in the case when a specific, severe washing operation is used. In this way the label is not permanent, however it has all the advantages of a permanent imprint, for example a silk screen, without the disadvantages thereof, such as the high costs thereof in terms of investments and energy requirements, inflexibility and low number of colors.
The selection of the adhesive to be used in adhering the label image to the crate surface will at least partly depend on the intended service life of the label, one-way or multiple trip use. Of course the adhesive must remain removable during crate washing. The adhesive must have been activated prior to or during application of the image to the crate. An easy and generally preferred method of applying the image is through the use of heat activatable adhesives, that have been applied to the image in the form of a reverse printed label. Other methods include the use of adhesives that can be activated through radiation, chemicals, electron-beam, micro-wave, UV and the like. It is also possible to use adhesives that can be activated through photo initiation, humidity, enzymatic action, pressure or ultra-sonic treatment.
It is preferred to use adhesives that are activated either by heat or by pressure. The latter case also encompasses adhesives, which require pressure to remain adhered, although they may have some tackiness without pressure. Preferred heat activatable adhesives have an initial tack temperature of not more than 90xc2x0 C., preferably between 70 and 87.5xc2x0 C.
The adhesive is preferably present on the back side of the image before it is applied to the crate surface. However, it is also possible to apply the adhesive to the crate prior to transferring the image. Another possibility is the use of inks in the image that have the adhesive incorporated therein.
The protective layer, if used, may be applied after the image has been transferred to the crate, for example using a conventional roller coater or spray system. In the alternative the protective layer may be part of the image material as it is transferred.
According to a further preferred embodiment the label layer consists of an image layer which is contained within containment layers, as described in the copending application of the same date titled: xe2x80x9cTransfer label having ink containment layers. container comprising a transfer layer and method of washing such a containerxe2x80x9d (attorney reference BO 40707), the contents of which application is incorporated herein by way of reference.
The label of the present invention may be applied to a substrate surface by a method comprising in its broadest form:
providing a surface, preferably moving at a uniform rate of speed,
presenting a reverse printed label according to the invention on a substrate, separable from its substrate, and
transferring the label ink to the polymeric surface.
The label is applied to a polymeric surface which has preferably been surface treated and temperature stabilized. The label is applied by transferring the ink from its film substrate utilizing a roller or a pad. Preferably a heated roller is used under pressure. As indicated previously, the adhesive may either be present on the label or may be on the polymeric surface. The adhesive has to be activated prior to or during transfer. Depending on the type of adhesive, the activation method will differ. The skilled person will be aware which type of activation will be required. In case of a pressure sensitive adhesive, pressure will be applied during transfer. If a heat activatable adhesive is used, it is preferred to preheat the polymeric surface, optionally in combination with a heated transfer system, such as a roller.
In a preferred embodiment a heat activatable adhesive is used, in combination with a heat-pretreatment of the polymeric surface. As the heat activated adhesive printed over the ink becomes tacky, the ink is released from the film substrate and adheres to the plastic surface.
The labels may be supplied on a roll, from which the images are transferred to the substrate, optionally in combination with a cutting operation. It is also possible to provide a stack of separate labels, using a suitable application device, such as a magazine fed labeler.
Depending on the requirements on the image it may be preferred to have a protective coating on top thereof. This coating may have been applied as part of the reverse printed label during image transfer. In a preferred embodiment the protective coating is applied after image transfer, for example by the use of a roller coater.
In that situation, the transfer surface is coated with a thin layer of protective coating, such as an acrylic wax. Subsequently a post treatment, preferably one or more heat treatments are given. With this treatment the label materials coalesce and without being bound thereto, it is assumed that the durable bond obtained thereby is affected through interdiffusion of the adhesive and plastic surface.
A label according to the present invention that combines sufficient durability during storage and use, with quick and economic removal, has preferably been heat treated after application to the container at a temperature of between 40xc2x0 C. and 100xc2x0 C., more preferably between 50xc2x0 C. and 90xc2x0 C.
In the case where the image has to be more durable, for example for multi-trip use, it is preferred to use either a more durable coating, such as a urethane or a cross-linked urethane, and/or a prolonged, more extensive post treatment.
It is well-known that polymeric materials and especially high density polyethylene in particular, are difficult materials to bond with adhesives. This invention describes a specific method of surface treatment to ensure adhesive bonding that is fast and economically.
An important discovery described in the invention is the coalescing of the label materials and surface coating by exposing the labelled area to very high temperatures for a few seconds to increase durability and resistance to moisture. This process alters the label composite from a series of adhered layers which are easily dissociated with immersion in water for two or more hours to a coalesced matrix of label adhesive, label inks and outer coating. During the heating the adhesive material inter diffuses with the plastic surface. The simultaneous coalescing and inter diffusion of this preferred embodiment of the invention result in a very durable label matrix. Resistance to water immersion can be varied from a few hours to several weeks by varying the time of exposure and the resultant temperature.
It should be noted, that the resistance to water immersion of an untreated label according to the invention may be sufficient as it never completely loses its bonding with the polymeric surface. The bonding only weakens; drying restores the bonding strength to its original value.
Having achieved the required label durability, it is also necessary to remove the label after it has served its purpose of identifying the contents of the container prior to consumption. The empty plastic containers and beverage bottles are returned to the beverage plant for refilling. The plastic containers are washed. During this wash the label must either be completely removed, or remain on the surface undamaged, depending on the situation (one-way or multi-trip).
In the former case, the heat treated adhesive used to bond the ink matrix, while durable in water, breaks down in the washing solution, preferably hot caustic, enabling the label and adhesive to be completely removed. The label residue is filtered out of the caustic solution. In the latter case the label is only removed when the washing conditions are changed to remove the label, for example by using a prolonged soaking and/or a stronger caustic solution, optionally in combination with the use of high pressure jets (liquid or gas).
Alternative methods for removing the images without a destructive treatment of the substrate (polymeric) surface comprise chemical removal (solvents), ultra sonic, sub-cooling, heating, brushing, enzymatic treatment, vacuum treatment, peeling and radiation, such as UV. Combinations of various methods are of course also possible.
The invention is also directed to a method of washing crates in order to remove the ink only label.
It may be desirable that the processing equipment be arranged so that the plastic containers are labelled in-line during the normal progression through the beverage facility, so that the crate label matches the bottle contents.